Scaling - Irregular patterns on the solder joint surface,  particularly of a
BGA ball, uniform in nature and resembling scales or flakes.


                    Causes:

                                a:  As a solder sphere moves from solid to
liquid, a volumetric change takes place uniformly across the surface of the
ball. The solder spheres received enough heat to begin to reflow, but the
heating process stopped, leaving the solder in its thixotropic or 'pasty'
phase on the tin/lead phase diagram. This solder did not reach the melt
point for the proper length of time resulting in lead weeping to the surface
in the form of lead flakes that are fully connected. Visible scaling can
indicate that insufficient heat was given to the joint in order to reach
complete reflow and to allow for enough activation energy to produce a
proper intermetallic bond. A lack of the intermetallic bond will lead to
premature joint failure.



                                b:  Cooling process too slow after the peak
reflow temperature was reached. This will lead to intermetallic growth and
tin/lead separation or a heavy concentration which shows up as a coarse
grain structure often resembling scales or flakes on the surface of a BGA
joint.


-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Wednesday, October 15, 2003 9:48 AM
To: [log in to unmask]; [log in to unmask]
Cc: [log in to unmask]
Subject: Re: [TN] BGA Scaling



Hi Dave! Can you further define "BGA Scaling"? Its a term I am not familiar
with.

Dave




                      Dave Chapman

                      <dchapman@CIRCUITS        To:       [log in to unmask]

                      ERVICE.COM>               cc:

                      Sent by: TechNet          Subject:  Re: [TN] BGA
Scaling
                      <[log in to unmask]>





                      10/14/2003 08:43

                      AM

                      Please respond to

                      "TechNet E-Mail

                      Forum."; Please

                      respond to Dave

                      Chapman










      -----Original Message-----
      From:  Dave Chapman
      To: [log in to unmask]
      Subject: Re: [TN]  BGA Scaling

      I am interested to find information on BGA scaling effect and
      solution, we saw this phenomena yesterday with a ERSA Scope
      demonstration. I have searched archives here and at SMTNET but no
      good information.
      Dave Chapman
      Circuit Service
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